The present invention relates to a control system for servo valve which controls opening degree of the servo valve having a plurality of servo coils used in the field of chemical plant or electric-power generating plant and a control method for the servo valve, and a combined-cycle electric-power plant and a gas turbine plant having the control system for servo valve.
In general, in the field of chemical plant or electric-power generating plant, a servo valve having a plurality of servo coils is used as a valve for controlling an important plant amount. Even if a break occurs in one of the servo coils, the servo valve having a plurality of servo coils can control the servo valve by compensating the break in the servo coil using the other sound servo coils, and this can prevent a shutdown or a power swing of the plant, which in turn can improves the reliability of the operation.
In order to perform the compensation of servo coil break, it is necessary to detect occurrence of a break in the servo coils. In the past, detection of wire break in the servo coil has been detected by a control operation unit such as a microcomputer outputting a servo control voltage demand based on an opening degree difference between a target opening degree and a real opening degree of the servo valve. This technology is disclosed, for example, in Japanese Patent Application Laid-Open No.9-126351.
In addition, there is proposed a method in which a break detecting resistor is connected to a plurality of servo coils in common, and a break in the servo coil is detected by a voltage of the break detecting resistor.
Since the technology disclosed in Japanese Patent Application Laid-Open No.9-126351 detects a break in servo coils using the control operation unit such as a microcomputer, the detection is dependent on the operation cycle, and accordingly there is a problem in the high speed operability. Since the operation cycle (sampling cycle) is 50 ms to 100 ms, the technology can not cope with the requirement of 5 ms.
On the other hand, the technology of using the common break detection resistor to the plurality of servo coils has a problem in that when a failure occurs in the common break detection line, the function of break detection is lost.
An object of the present invention is to provide a control system and a control method for servo valve which can stably continue to control a servo valve when a break occurs in servo coils of a servo valve having a plurality of servo coils, and to provide a combined-cycle electric-power generating plant and a gas turbine plant having the control system for servo valve.
The present invention is characterized by that a break in a servo coil is detected by a voltage in each of a plurality of servo coils.
A preferred embodiment of the present invention is that detection of wire break in the servo coil and compensation of wire break are performed by servo amplifiers.
That is, since a break in the servo coil is detected by a voltage in each of a plurality of servo coils, the break can be instantaneously detected. Further, since the compensation of wire break in the servo coil is performed by sharing the load current of the broken servo coil among the unbroken servo coils, the control of servo valve can be stably continued.